It is common practice for plastics or rubber tubes to be inserted into the tissues, cavities, orifices or veins of the human body.
Such tubes (otherwise known as catheters or cannulae) possess two channels down the central bore of the catheter. Whilst one (the larger) channel, is used for the infusion of fluid into or drainage out of the body, the other smaller diameter channel communicates with a latex balloon placed concentrically around the catheter shaft and close to the end of the tube which is left within a body cavity, e.g., the urinary bladder.
The other end of the smaller channel is protected by a plastic hub containing a displaceable rubber diaphragm which acts as a one-way valve. This secondary channel and valved-port permits the inflation of the balloon which then effectively engages upon the surrounding tissues of the body cavity and prevents the catheter from sliding out of the body.
The technique and procedure for inflating the balloon at the present time, involves a series of actions on the part of a nurse or doctor, including the manipulation and breaking open of an ampoule or bottle or sterile water or saline; the opening of a sterile packet containing an hypodermic type plastics syringe; the opening and use of a sterile needle or plastics quill from a packet to aspirate the contents of the ampoule into the syringe; and finally the insertion of the nozzle of the full hypodermic into the valved-inflation port of the catheter.
Moreover the resistance of the valve diaphragm must be overcome and a precise volume of fluid discharged into the balloon to achieve inflation, before the hypodermic syringe is removed from the inflation port.
It can be easily seen from the above that numerous components are required to perform the task and the risk of bacterial contamination during the various stages is an ever present potential problem.
Similarly, another common and important function of plastics tubes which have been partially inserted into the body is their use as a portal for access to the venous or arterial system.
In these circumstances, a short length of fine-calibre hollow plastics or rubber tubing is placed, by a variety of techniques, into the lumen or channel of a blood vessel through a small wound in the skin. The central channel of the hollow catheter thereby is able to conduct a variety of physiological fluids into the blood vascular system.
The ends of the cannulae external to the body surface are fitted with a plastics or metal female luer hub which conforms to an International Standard in respect of its internal configuration.
Into this female luer hub, can be fitted a male luer nozzle which also conforms to an International Standard specification.
The normal practice is for the male nozzle to be the end component of an infusion tubing system which slowly delivers fluid from an intravenous bottle or bag, under the influence of gravity or a mechanical roller-pump. At intervals, in the care of patients, the need for the infusion system can be dispensed with, in order to make the patients more mobile and allow them to walk freely about the wards and corridors.
To achieve this end, the female hub of the intravenous cannula is covered by a small plastics cap or plug. However, before this is performed, the cannula tubing must be filled with a saline solution (often containing an anticoagulant agent--heparin) to prevent coagulation of the blood within the cannula and adjacent blood vessels.
This procedure, as in the case of the catheter balloon inflation manoeuvre, also requires the same range of accessory equipment to be used as previously described in the preceding paragraphs, to accomplish the final objective.